1. Field of the Invention
The present invention relates to nuclear medicine studies of a patient's heart and more particularly to myocardial perfusion SPECT studies.
2. Description of the Prior Art
In SPECT myocardial perfusion study, a diagnostician examines a nuclear medicine image of a patient's myocardium (heart muscle) to see which areas of the heart take up a radioisotope which is introduced into the patient's bloodstream. If any region of the heart does not take up the radioisotope, that region is not perfused by blood and the tissue in that region is dead. If the region does take up the radioisotope, but not to the same extent as other regions, that region is affected by arteriosclerotic disease.
Myocardial perfusion studies are always carried out on the patient's left ventricle because of the importance of this muscle in pumping blood throughout the body. It is therefore important to identify the precise location of any diseased or dead myocardial tissue within the left ventricle. In order to do so, it is conventional practice to reference the position of a tissue region to the oblique axis of the left ventricle.
One of the critical stages in defining the oblique axis is the localization of the heart from the reconstructed volume and the selection of a most suitable representative slice (MSRS) among all transverse slices along the long axis of the patient's body, either in manual or automatic processing myocardial perfusion SPECT studies. The MSRS is a transverse slice which contains a U shaped left ventricle cross section having the best separation of its two sides of the left ventricle wall. Based upon the MSRS, a center line can be defined such that it bisects the U shaped left ventricle cross section into two approximate equal parts along the long axis of such a cross section. After the center line is defined, the other following stages required to define the oblique axis can be implemented.
At the present time, the localization of the heart and the selection of the MSRS is performed manually according to the technician's subjective judgement. This is a tedious process which requires the user to display a whole set of reconstructed transverse slices on the screen and to visually examine the slices one by one. Thus, even studies conducted on the same patient, by the same technician, may not be exactly comparable with respect to each other. Furthermore, subjective judgement depends on the operator's skill, knowledge and other human factors. Errors, inconsistency, and bias may be introduced, therefore, it would be an advantage if the localization of the heart and the selection of the MSRS could be automated.
U.S. Pat. No. 5,381,791 entitled "Automatic Identification Of Anatomical Features Of Interest From Data Acquired In Nuclear Medicine Studies And Automatic Positioning Of Scintillation Cameras To Carry Out Such Studies At Optimal Positions" describes scanning a nuclear medicine image and identifying and correlating with each other, pixels of maximum and minimum intensity. This information is used to define a region of interest in which an anatomical feature of interest may be located. U.S. Pat. No. 5,421,331 entitled "Automatic Identification Of The Long Axis Of The Left Ventricle From Nuclear Medicine SPECT Data For Use In Myocardial Perfusion Studies" describes identifying and correlating local minima and maxima in images of slices of the left ventricle. The entire disclosures of the above patents are hereby incorporated by reference as if fully set forth.
One object of the present invention is to provide a system that automatically localizes the patient's heart from the reconstructed volume for further processing without the need for any user intervention.
Another object of the present invention is to provide a system for automatically selecting the MSRS among all of the reconstructed transverse slices without the need for any user intervention. The present invention could then be used as one of the key components in automatic myocardial perfusion SPECT processing systems or it could be used as a separate tool by the technician in the manual processing of myocardial perfusion SPECT studies.